The proposed objective of this application relates to the study of the regulation of the cysteinyl leukotrienes by investigation their biosynthesis. This work has a significant impact on hyperresponsiveness of airways, particularly bronchial asthma, which acts over 3 million Americans. The cysteinyl leukotrienes (leukotrienes C4, D4, and E4) are lipid mediators implicated in the pathogenesis of this disease. Leukotriene C4 synthase catalyzes the first committed step in the formation of the cysteinyl leukotrienes by the conjugation of leukotriene (LT)A4 with reduced glutathione (GSH) to form leukotriene C4. The goal of this proposal is to characterize LTC4 synthase. The full length cDNA has been expressed in COS-7 cells and sf9 insect cells, yielding substantial amounts of biologically active enzyme. From these sources, the enzyme will be purified and its biochemical characteristics studied by kinetic analysis and compared to that of the native enzyme. Site-directed mutagenesis of the putative eicosanoid binding site and active site will elucidate the role of specific amino acids involved in the catalytic mechanism. Polyclonal antibodies have been raised to study the subcellular and cellular distribution as well as the distribution of LTC4 synthase in normal and asthmatic lungs. The final objective of this proposal will be to clone the human gene for LTC4 synthase, which will permit future studies of genomic regulation.